Several different kinds of systems and arrangements of the type defined in the introduction are known to the art.
For instance, it is known to supervise tunnels, such as tunnels intended for railtrack vehicles, automotive vehicles, and the like, to distribute TV cameras or sensors, normally one-category sensors, along the length of the tunnel and to supervise ocularly the flow of traffic and any hazard moments and hazard situation that may arise, by one or more operators at a supervising table or monitoring table.
This system is based on the ability of the actual operators to establish that a hazard exists, such as a fire hazard, and themselves determine the level of the hazard and its location and to determine the need for activating one or more of a plurality of available measures or actions.
There have also been proposed a number of different systems for coupling a plurality of sensors to a control unit that includes computer equipment and built-in threshold values, where an alarm signal is initiated and sent from the computer equipment to an operator immediately one of the connected sensors indicates a measurement value or a value related to a hazard level that exceeds a predetermined and current threshold value.
It is also known to explore manually the measure or measures, or the action or actions, that shall be undertaken or carried out in response to information delivered by one and/or more activated sensors.
The most drastic action that can be considered applicable in such a situation is to close the tunnel to traffic, to call the police and fire brigade for relevant action when a single sensor is activated. Such action will cause a train or cars and other vehicles present in the tunnel to be enclosed therein.
Other drastic actions involve stopping a train inside the tunnel and evacuating train passengers through the tunnel, hopefully in the correct direction relative to the ongoing hazard situation.
The complexity of the problem naturally increases when several trains are situated within one and the same tunnel section, and increases still further when a number of railway stations are included within the extension of an underground railway system (subway system).
The last mentioned application should also take into account the air currents that normally exist and the strong, more prevailing air flows or air streams that are generated by movement of a train through the tunnel system.
Earlier known systems and arrangements of the present nature have the drawback of not being able to readily observe the time-wise development of a hazardous situation and the value or magnitude of a current or ongoing hazard level.